The purpose of this Phase I proposal is to develop a mammalian cell culture aneuploidy assay using the CAK mouse cell line. While a great number of short term assays have been developed to detect compounds which induce either gene mutations or chromosomal damage, little research has focused on the development of short term assays to detect aneuploidy. The development of a mammalian cell culture assay to detect aneuploidy would play a crucial rule in detecting chemicals which may cause either birth defects or cancer in humans. The CAK line is extremely useful for this purpose since it is a near diploid line, and a selective system can be developed in which aneuploidy can be detected using resistance to 2,6-diaminopurine (DAP). This eliminates the need to detect aneuploidy by comparing the distribution of chromosomes in treated and untreated cells. A clone of CAK cells, CAK-B3 Toy(r)-13, is heterozygous for a physical marker on chromosome 8, which carries the adenine phosphoribosyl transferase gene. The major goal of this project is to establish a CAK line which is heterozygous for both APRT and for the physical marker on chromosome 8. The gene coding for APRT would then be linked to a chromosome which can be easily identified in metaphase preparations. The clone which is heterozygous for both the physical marker on chromosome 8 and for APRT activity can be used to screen chemicals either for their ability to induce mutations or induce aneuploidy. Resistant cells to DAP (presumably APRT-) will be examined for loss of the chromosome carrying the APRT+ allele which is a demonstration of aneuploidy. This is in contrast to induction of mutations to APRT- in which both the physically normal and abnormal chromosome 8 would be present in resistant cells. The successful development of a relatively inexpensive, rapid screening test for these end-points (aneuploidy, tumor promotion) would be a significant addition to current in vitro screening batteries and could significantly lessen the overall cost (to both the government and private sector) of determining the safety of new chemicals and drugs. Thus, the assay developed under this project will become a valuable resource asset to the NIH, NIEHS and other government agencies involved in protecting human health.